Prostaglandin E1 was studied for its effects on protein and glycoprotein metabolism in rat parathyroid glands. Concentration of PGE1 (100 micron g/m1) produced significant decreases in the incorporation of radiative uridine and thymidine into RNA and DNA respectively. A similar dose failed to alter the incorporation of radioactive fucose or amino acids into cellular glycoprotein or protein. However, this dose and lower doses (0.0001 micron g/ m1) did inhibit secretion of immunological parathyroid hormone. Cortisol and vitamin A appeared to block this effect of PGE (0.01 micron g/m1) on secretion of radioactively labeled parathyroid hormone and of the specific glycoprotein.